Polysuccinimides, polyaspartates and copolymers thereof are becoming increasingly useful as mineral scale inhibiting agents, nutrient absorption enhancers, additives for cosmetics and personal care products, adhesives, anti-redeposition agents for detergents, dispersants, additives for paper making, corrosion inhibitors, metal working fluids, lubricants for conveyor belts, additives for the prevention of encrustation in sugar manufacture, and tartar preventative agents in toothpaste.
Methods are known for the production of polysuccinimide by the polymerization of aspartic acid in the presence of various catalysts, such as phosphoric acid and sulfur-containing dehydrating agents and the like. However, these prior art methods rely on an inefficient process of heat transfer during polymerization, namely the heating of an unstirrable melt. Another disadvantage to these methods is the large amount of catalyst and/or dehydrating agent which is required for polymerization to occur and the subsequent removal of the excess catalyst.
Attempts to perform catalytic polymerizations as stirrable, liquid reactions have been made, but again exceedingly high amounts of catalyst were required to achieve the polymerization of desirable high molecular weight products (U.S. Pat. No. 5,484,945 to Nagatomo et al.).
There is an ongoing need therefore, for a convenient method of catalytically polymerizing aspartic acid to polysuccinimide in high yield, purity and of desired high molecular weight. The present inventive method satisfies this need and overcomes the disadvantages of the prior art methods.